This invention relates to a control circuit for automatically deenergizing electric heating elements operating in a cooking environment, such as in an electric deep fat fryer or in an electric oven, responsive to an over temperature condition.
In restaurant cooking equipment, such as deep fat fryers for example, there is normally a container filled with cooking fat heated to a set cooking temperature, most often in excess of 250.degree. F, and an operating thermostat sensing the cooking fat temperature cycles the heating means on and off to maintain the set temperature. In an electric deep fat fryer, power to the electric heating elements is controlled by a contactor having a set of high capacity contacts opened and/or closed by a coil connected in a low power control circuit with a set of switch contacts actuated by the operating thermostat. Most safety regulations further require a high temperature safety control which functions if the operating control fails and which is designed to terminate input power only if high unsafe temperatures are sensed.
U.S. Pat. No. 3,824,373 issued July 16, 1974, to Clarence H. Napier illustrates a safety control circuit for a deep fat fryer which incorporates two control contactors each having high-current contacts connected in series with the heating elements, and the operating coils for the separate contactors are controlled, respectively by the operating thermostat and by a high temperature safety thermostat. However, since the safety contactor contacts are never shifted except responsive to an over temperature condition, if the contacts should become fused together, the fact that the safety thermostat signalled an unsafe condition would not necessarily assure that input power to the heating elements had been terminated.